﻿49 
  

  

  sharply 
  separated 
  than 
  at 
  the 
  preceding 
  stage, 
  and 
  a 
  vesicle 
  

   has 
  made 
  its 
  appearance 
  in 
  each. 
  After 
  two 
  minutes 
  and 
  a 
  

   half, 
  19, 
  these 
  three 
  micromeres 
  have 
  flattened 
  down 
  against 
  

   each 
  other 
  and 
  against 
  the 
  compound 
  mass, 
  so 
  that 
  the 
  egg 
  is 
  

   once 
  more 
  nearly 
  spherical. 
  This 
  stage 
  may 
  be 
  called 
  the 
  

   third 
  period 
  of 
  rest. 
  

  

  This 
  hgure 
  and 
  the 
  one 
  before 
  it 
  are 
  from 
  the 
  same 
  egg, 
  as 
  

   indeed 
  are 
  all 
  the 
  iigiires 
  on 
  this 
  plate 
  except 
  25, 
  27 
  and 
  28 
  ; 
  

   but 
  after 
  Figure 
  18 
  had 
  been 
  'sketched, 
  the 
  egg 
  rotated 
  a 
  little, 
  

   and 
  Figure 
  19 
  is 
  a 
  view 
  at 
  right 
  angles 
  to 
  all 
  the 
  preceding 
  

   ones. 
  

  

  The 
  vesicles 
  are 
  seen 
  to 
  be 
  a 
  little 
  larger 
  than 
  they 
  were 
  a 
  

   few 
  minutes 
  before, 
  but 
  I 
  did 
  not 
  succeed 
  in 
  seeing 
  them 
  dis- 
  

   appear 
  at 
  this 
  stage. 
  

  

  The 
  egg 
  which 
  was 
  figured 
  remained 
  in 
  the 
  condition 
  shown 
  

   in 
  Figure 
  19 
  for 
  thirteen 
  minutes, 
  and 
  during 
  this 
  time 
  it 
  

   rotated 
  back 
  again 
  into 
  the 
  position 
  which 
  it 
  had 
  occupied 
  at 
  

   first. 
  

  

  At 
  the 
  end 
  of 
  thirteen 
  minutes 
  the 
  three 
  micromeres 
  c, 
  d, 
  d, 
  

   again 
  became 
  conspicuous; 
  the 
  compound 
  mass, 
  a 
  and 
  h, 
  

   elongated, 
  and 
  a 
  surface 
  depression 
  separated 
  the 
  portion 
  b 
  

   from 
  the 
  portion 
  a, 
  and 
  the 
  first 
  micromere, 
  a, 
  quickly 
  divided 
  

   into 
  two, 
  as 
  shown 
  in 
  Figure 
  2U. 
  

  

  By 
  moving 
  the 
  cover-glass, 
  I 
  managed 
  to 
  rotate 
  the 
  eggs 
  a 
  

   little, 
  and 
  to 
  get 
  a 
  sketch. 
  Figure 
  21, 
  in 
  the 
  same 
  position 
  

   as 
  Figure 
  19. 
  Figure 
  21 
  is 
  one 
  minute 
  later 
  than 
  Figure 
  20, 
  

   and 
  it 
  will 
  be 
  seen 
  that 
  the 
  second 
  micromere, 
  h, 
  and 
  two 
  of 
  

   the 
  others, 
  have 
  already 
  begun 
  to 
  flatten 
  down 
  and 
  to 
  pass 
  

   into 
  the 
  resting 
  condition. 
  

  

  From 
  this 
  time 
  on 
  I 
  was 
  not 
  able 
  to 
  keep 
  the 
  egg 
  under 
  

   constant 
  observation, 
  but 
  examined 
  it 
  at 
  short 
  intervals. 
  A 
  

   well 
  marked 
  resting 
  period 
  follows 
  the 
  stage 
  shoM-n 
  in 
  Figure 
  

   21, 
  but 
  as 
  it 
  presents 
  no 
  new 
  features, 
  it 
  was 
  not 
  figured. 
  

   Figure 
  22 
  is 
  fifteen 
  minutes 
  later, 
  and 
  shows 
  the 
  egg 
  at 
  the 
  

   fourth 
  period 
  of 
  activity. 
  There 
  are 
  now 
  two 
  more 
  micro- 
  

   meres, 
  which 
  appear 
  to 
  be 
  formed 
  by 
  the 
  two, 
  c 
  c, 
  Figure 
  20, 
  

   which 
  were 
  produced 
  during 
  the 
  third 
  period 
  of 
  activity 
  by 
  

   the 
  division 
  of 
  the 
  first. 
  Figure 
  14, 
  g. 
  

   4 
  

  

  